1. Field of the Invention
This invention relates to the field of profiling devices. More particularly, this device relates to profiling devices capable of performing contour and surface profiling by means of a cutter device controlled by signals received from a sensing device which senses the movement of a tracer spindle.
2. Description of the Prior Art
In the past, profiling devices (for example, Japanese Patent Kokai No. 49-125983) were useful for contour profiling (X-Y axis profiling). Such devices are comprised of a vertical spindle which eccentrically fits a stylus, said spindle being designed to rotate in a clockwise or counter-clockwise direction when the rotating stylus contacts a model. In such devices, when the electric motor for the spindle rotates in a clockwise and then counterclockwise direction, there is created a large change of rotational speed. Such devices generally operate by rotating the spindle in the clockwise-to-zero-to counterclockwise-to-zero rotation and continually repeat this process. During this process, the heavy rotating parts (such as the rotor of the motor, the reduction gear, the spindle and the stylus) are subjected to tremendous changes in rotational speed which create substantial amounts of rotational inertia which must be absorbed by the device. The continual absorption of such energy results in wearing down and eventually destroying the machine. Also, in such devices, the rotational speed of the spindle cannot respond immediately to contract with the model. Consequently, the profiling accuracy of such a device is not satisfactory.
In a conventional surface profiling device (X-Z axis profiling), different types of problems are encountered. When the inclination of the vertical spindle is detected by a differential transformer, the cutter cannot closely mirror the movement of the stylus. In such devices, the cutter moves further into the workpiece than the stylus is moving against the model. Thus, deeper cuts than are desired are made in the workpiece and thus large amounts of compensation is allowed for. However, when such compensation is allowed for in one direction, even a greater error results in the opposite direction. When the stylus of such a prior art device profiles a horizontal plane having a steep slope thereon, the core of the differential transformer developes a large displacement from the positive position relative to the minus position. When this occurs, the cutting accuracy of the device is impaired, especially at the points on the workpiece where the cutting device is supposed to turn sharply. This is true because the differential transformer has been displaced so far to the positive position that there is a significant reaction time required in order to bring it into the minus position.
Also, since the stylus in a conventional surface profiling device is permitted to oscillate somewhat with respect to the tracer body, additional accuracy problems result. The disadvantage of this feature is apparent when profiling a workpiece in two axial directions perpendicular to each other. The stylus is kept in contact with the horizontal plane of the table on which a model and a workpiece are fixed. The table is fed to the right until the stylus hits against the right side of the ascending slope of the model. When this occurs, the stylus inclines slightly towards the right and, consequently, the cutter goes ahead of the stylus to an extent equal to the displacement caused by the inclination of the stylus. Accordingly, it is impossible to produce a workpiece in the same dimensions as the model. Some error may be compensated for by designing a stylus somewhat thicker than the cutter. However, when the thicker stylus reaches the descending slope, the inclination of the stylus is nearly cancelled. When the cutter is advanced a distance equal to the increased thickness of the stylus, the cutter has already moved beyond a point where the workpiece should be cut. Thus, the workpiece will not be cut at all or will be cut at a point beyond where it should be. For example, the table is fed to the left until the stylus touches the left ascending slope of the model. Then the left descending slope is cut accurately, but the right descending slope of the model is left uncut. Accordingly the roughness on the descending slope of the workpiece is twice as inaccurate as it normally would be in the case of a device not using such a compensative mechanism. Thus, the resulting product requires an enormous amount of finishing work.